Systems and methods for detecting tissue contact and needle penetration depth

ABSTRACT

Systems and methods for determining tissue contact and penetration depth are provided. In one aspect, the system includes a needle and a pressure measurement assembly. The needle, in one exemplary embodiment, includes a first end and a second end with at least one aperture located a predetermined distance from the first end. The pressure measurement assembly is connected with a portion of the needle to measure pressure of fluid flowing through the needle. The pressure measurement assembly measures a first pressure when the needle contacts tissue and a second difference in pressure when the needle penetrates the tissue and the aperture becomes occluded. 
     In an alternative aspect, the system includes a needle and a sensor. The sensor, in another exemplary embodiment, is coupled with a portion of the needle to detect tissue contact pressure on the sensor as the needle penetrates tissue and makes contact with the sensor. The sensor is located a predetermined distance from the first end of the needle.

FIELD OF THE INVENTION

The invention relates generally to needles, and more particularly, to asystem and method for detecting tissue contact and needle penetrationdepth.

BACKGROUND

Drug delivery systems currently exist that supply therapeutic substancesthrough a needle to regions of a patient's body. Such regions mayinclude a diseased blood vessel, body cavity or organ. In the case of adiseased blood vessel, for example, the therapeutic agent may be used totreat an arterial lesion and/or to promote an angiogenic response

In some applications, a needle may be connected to a catheter assemblyto deliver the therapeutic agent deep into the body. In thisapplication, it is often difficult to determine when the needle contactsthe organ, cavity wall, or vessel wall. Further, it is difficult todetermine the penetration depth of the needle. In many of theapplications for which a needle catheter assembly is used to delivertherapeutic agents to regions within the body, the agent must bedelivered to a precise location. Accordingly, it is desirable to providefeedback that indicates when the needle contacts the cavity or vesselwall and when the needle has been inserted to a predetermined depth.

SUMMARY OF THE INVENTION

Systems and methods for determining tissue contact and penetration depthare provided. In one aspect, the system includes a needle and a pressuremeasurement assembly. The needle, in one exemplary embodiment, includesa first end and a second end with at least one aperture located apredetermined distance from the first end. The pressure measurementassembly is connected with a portion of the needle to measure pressureof fluid flowing through the needle. The pressure measurement assemblymeasures a first pressure when the needle contacts tissue and a seconddifference in pressure when the needle penetrates the tissue and theaperture becomes occluded.

In an alternative aspect, the system includes a needle and a sensor. Thesensor, in another exemplary embodiment, is coupled with a portion ofthe needle to detect tissue contact pressure on the sensor as the needlepenetrates tissue and makes contact with the sensor. The sensor islocated a predetermined distance from the first end of the needle.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings in which:

FIG. 1 illustrates a side cross-sectional view of one embodiment of afluid delivery catheter;

FIG. 2 illustrates the embodiment of the fluid delivery catheter of FIG.1 where the needle penetrates tissue;

FIG. 2 a illustrates an alternative embodiment of a fluid deliverycatheter where a needle penetrates and extends into tissue beyond thevessel wall;

FIGS. 3 a-3 c illustrate the embodiment of the fluid delivery catheterof FIG. 1 in different positions with respect to the tissue;

FIG. 4 illustrates a graph representing different fluid injectionpressure measurements within the needle corresponding to variouspositions of the needle with respect to the tissue as shown in FIGS. 3a-3 c;

FIG. 5 illustrates a front view of one assembly for measuring thepressure of the fluid in the needle;

FIG. 6 illustrates a front view of an alternative assembly for measuringthe pressure of the fluid in the needle;

FIG. 7 illustrates a side cross-sectional view of an embodiment of afluid delivery catheter with a force transducer;

FIGS. 7 a and 7 b illustrate the embodiment of the fluid deliverycatheter of FIG. 7 in different positions with respect to the tissue;

FIG. 8 illustrates an enlarged view of the embodiment of the needle andthe force transducer shown in FIG. 7;

FIG. 9 a illustrates an enlarged view of an alternative embodiment of aneedle for use in the fluid delivery catheter shown in FIG. 7;

FIG. 9 b illustrates an enlarged view of an alternative embodiment of aforce transducer for use in the fluid delivery catheter shown in FIG. 7;

FIG. 9 c illustrates an enlarged view of the needle of FIG. 9 a and theforce transducer of FIG. 9 b;

FIG. 10 illustrates a front view of one embodiment of a piezoelectricforce transducer connected to the second end of a needle; and

FIG. 11 illustrates a flow diagram of one embodiment of a process fordetecting tissue contact and needle penetration depth.

DETAILED DESCRIPTION

Systems and methods for detecting tissue contact and needle penetrationdepth are described. In the following detailed description of thepresent invention, numerous specific details are set forth in order toprovide a thorough understanding of the present invention. However, itwill be apparent to one skilled in the art that the present inventionmay be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention. Several exemplary embodiments are described herein, and itwill be appreciated that alternative embodiments exist within the scopeof this invention.

FIG. 1 illustrates a side cross sectional view of one embodiment of afluid delivery catheter 100. The fluid delivery catheter 100 can be usedto provide therapeutic agents to a particular region of a patient'sbody, for example, to prevent or treat arterial disease (e.g. arterialstenosis or restenosis). The fluid delivery catheter 100 can be anymedical device designed for insertion into a region of a patient's bodyto permit injection of fluids. It is contemplated that the fluiddelivery catheter has applicability for use with any region within apatient's body, including blood vessels (e.g. coronary arteries),urinary tract, intestinal tract, kidney ducts, and the like.

In FIG. 1, the fluid delivery catheter 100 includes a needle 130 withina needle sheath 110. The needle sheath is mounted on a dilatationcatheter 120. The fluid delivery catheter 100 is shown within a cavity160 of a patient's body in FIG. 1. The cavity 160 may be a lumen of ablood vessel, such as a coronary artery. The fluid delivery catheter 100is maneuvered over a guidewire 114. The guidewire directs the fluiddelivery catheter 100 through torturous passageways within the body toarrive at the desired body cavity 160. The dilatation catheter 120 has aballoon 112 that inflates and directs the needle tip 132, which isextendable, toward body tissue such as a blood vessel wall 150.

The needle 130 includes a needle tip 132 and an aperture 134 located apredetermined distance from the needle tip 132. As the needle 130 isinserted into body tissue, first the needle tip 132 and then theaperture 134 become occluded. This is shown in FIG. 2. The occlusion ofthe needle tip 132 and aperture 134 increase the injection pressure ofthe fluid within the needle 130, thereby allowing an operator todetermine tissue contact and penetration depth of the needle 130.

In one embodiment the needle 130 may include more than one aperture 134spaced in predetermined measurements from the needle tip 132 of theneedle 130. For example, a first aperture 134 may be located a firstpredetermined distance from the needle tip 132. A second aperture (notshown) may be located a second predetermined distance from the firstaperture 134. In alternative embodiments, there may be more than twoapertures.

In one embodiment, the space between the apertures may be the same. Inother alternative embodiments, the distances between the apertures maybe different. In another embodiment, the apertures may all be the samesize and shape while in another embodiment the sizes and shapes of theapertures could be different. The apertures should be much smaller thanthe needle tip 132 lumen so that the fluid will be ejected from theneedle tip 132 rather than the aperture 134. The occlusion of both theneedle tip 132 and individual aperture 134 and the concomitant increasesof injection pressure allow an operator to determine the penetrationdepth of the needle 130 as it becomes embedded in the vessel wall 150.

FIG. 2 illustrates the embodiment of the fluid delivery catheter 100 ofFIG. 1 where the needle 130 is shown penetrating a vessel wall 150. Asthe needle tip 132 contacts the vessel wall 150, the needle tip 132becomes occluded. Then, as the needle 130 further penetrates the vesselwall 150, the aperture 134 that is located a predetermined distance fromthe needle tip 132 becomes occluded. Accordingly, in alternativeembodiments, the predetermined distance between the needle tip 132 andaperture 134 may vary according to what the desired penetration depthmay be.

In one embodiment, injection pressure measurements are takencontinuously as a therapeutic agent is injected from the first end of aneedle, through the needle 130, and to the needle tip 132.

As the vessel wall or other tissue within the body occludes the needletip 132, an increase in pressure will occur. Accordingly, an operator isable to determine by the increase in fluid pressure that the needle tip132 has contacted the vessel wall. As the vessel wall or other tissueoccludes the aperture 134, another increase in fluid pressure willoccur. An operator is again able to determine by the second increase inpressure that the needle 130 has been inserted to a predetermined depthin the tissue or vessel wall 150.

FIG. 2 a illustrates an alternative embodiment of a fluid deliverycatheter 200 where a needle 230 penetrates and extends into tissue 270beyond the vessel wall 250. In FIG. 2 a, the needle 230 includes morethan one aperture. The first aperture 234 is located a predetermineddistance from the needle tip 232 so that occlusion of the first aperture234 indicates penetration of the needle 230 a certain depth into thefirst tissue layer or vessel wall 250. The second aperture 236 islocated a predetermined distance from the first aperture 234 so that theocclusion of the second aperture 236 indicates a further penetration ofthe needle 230. In some cases, an operator may have knowledge about thethickness of certain tissue. For example, the vessel wall 250 may be aknown thickness. The second aperture 236 may then be placed according tothat known thickness so that occlusion of the second aperture 236indicates the needle 230 has penetrated all the way through the firstlayer of tissue 250 and into the second layer of tissue 270.

FIGS. 3 a-3 c illustrate the embodiment of the fluid delivery catheter100 in different positions with respect to the vessel wall 150. FIG. 3 aillustrates the fluid delivery catheter 100 where the needle 130 has notyet contacted the vessel wall 150. The needle tip 132 is close to andproximate to but not contacting the vessel wall 150.

FIG. 3 b illustrates the fluid delivery catheter 100 where a portion ofthe needle tip 132 is contacting and has become embedded in the vesselwall 150. However, the needle 130 has not been fully inserted into thevessel 150. Accordingly, as seen in FIG. 3 b, the desired penetrationdepth of the needle 130 has not been achieved.

FIG. 3 c illustrates the fluid delivery catheter 100 where the needle130 has penetrated the vessel wall 150 to a predetermined depth. Thedesired penetration depth has been achieved when the vessel wall 150occludes the aperture 134. As seen in FIG. 3 c, both the needle tip 132and the aperture 134 are embedded within the vessel wall 150.Accordingly, as discussed above, an operator is able to determine by theincrease in injection pressure caused by the occlusion of the aperture134 that the needle 130 has penetrated tissue to a predetermined depth.

FIG. 4 illustrates a graph representing different pressure measurementsof fluid within the needle 130 taken at the three needle positions shownin FIGS. 3 a through 3 c. The graph is representative of pressure versustime where it is assumed that the needle 130 is pushed into vessel wall150 over time in the sequence shown in FIGS. 3 a (first), 3 b (next),and 3 c (last). As the needle 130 is in the body cavity 160 as seen inFIG. 3 a but not contacting the vessel wall 150, the injection pressureis lower than the scenarios shown in FIGS. 3 b and 3 c. This pressuremeasurement is shown as region A 410 in FIG. 4. As a portion of theneedle tip 132 penetrates the vessel wall 150, an increase in pressureoccurs. The pressure increases dramatically after the needle tip lumen132 becomes occluded, but the rate decreases slightly shortly thereafteras shown in region B 420 in FIG. 4. As the needle 130 penetrates thetissue or the vessel wall 150 a predetermined depth and the aperture 134becomes occluded, a second dramatic increase in pressure is detected.This pressure spike is shown as region C 430 in FIG. 4. Although only 3points are shown in FIG. 4 corresponding to FIGS. 3 a 3 b and 3 c, ifadditional apertures were to be added on the needle, additional pressureincreases would occur as each aperture became occluded.

FIG. 5 illustrates a front view of one embodiment of a pressuremeasurement assembly 500 connected to a needle 130. In one embodiment,as shown in FIG. 5, the pressure measurement assembly 500 includes asensor 512 to measure pressure.

As seen in FIG. 5, one end of the pressure measurement assembly 500 isconnected to a syringe 514. A syringe pump 612 in FIG. 6 is used toinject the fluid from the syringe 514 and through the needle 130 at aconstant, controlled rate. In one embodiment, the sensor 512 detects afirst injection pressure increase as the needle tip contacts tissue. Thesensor 512 measures a second injection pressure increase as the needle130 penetrates the tissue to a predetermined depth. The second injectionpressure increase occurs as the aperture in the needle (shown in FIGS.1-3) becomes occluded, thereby increasing the pressure of thetherapeutic agent being injected into the tissue.

An example of a pressure measurement assembly 500 that may be utilizedwith the present invention is a disposable pressure monitoring systemmanufactured by Utah Medical Products, Inc. The assembly 500 may easilybe attached to a luer lock attached to the proximal end of the needle130. The disposable pressure monitoring system provides fluid pathvisualization. Different manufacturers may also produce similar pressuremeasurement systems that are capable of being utilized in the context ofthe present invention. Alternatively, a much smaller sensor assembly canbe integrated directly into the needle assembly. For example, a smallerversion of the sensor 512 could be mounted onto a small plasticconnector that is used to attach the needle to the syringe.

FIG. 6 illustrates a front view of an alternative embodiment of apressure measurement assembly 600 connected to the proximal end of theneedle 130. The pressure measurement assembly 600 includes a signalprocessor and pressure display 610. Here, a proximal end of a bifurcatedconnector 616 has a transducer port 620 and a connection port 622 thatconnects the bifurcated connector 616 to the syringe 618. The needle 130is connected to a distal end of the bifurcated connector 616. Thesyringe 618 is placed on a syringe pump 612.

The syringe pump 612 pumps a therapeutic agent at a constant ratethrough the needle 130. The therapeutic agent should be pumped veryslowly so that the amount of therapeutic agent that is dispensed beforethe needle reaches the desired penetration depth is minimized. As theneedle 130 advances and its tip makes contact with or penetrates tissue,the occlusion of the needle tip creates a first resistance to the flowof the therapeutic agent. This is detected by the pressure sensor 624.Accordingly, the increase in pressure indicates that the needle 130 hascontacted tissue.

The operator continues to advance the needle 130 until the tissue beginsto occlude the aperture (shown in FIGS. 1-3) of the needle 130. As theaperture becomes fully occluded, this increases the resistance to theflow of the therapeutic agent and results in a second pressure increaseas shown in region C in FIG. 4.

FIG. 7 illustrates a side cross-sectional view of an alternativeembodiment of a fluid delivery catheter 800 including an attached straingauge 840. Similar to FIG. 1, the fluid delivery catheter 800 includes aneedle 830 within a needle sheath 810. The needle sheath 810 is attachedto a dilatation catheter 820. The dilatation catheter 820 is deliveredinto the body over a guidewire 814 that guides the dilatation catheter820 through tortuous pathways within a patient's body to a desiredregion or body cavity 860. The dilatation catheter 820 may include aballoon 812 that inflates and directs the distal end of the needlesheath 810 and needle 830 toward a vessel wall 850. The operator pushesthe needle 830 toward the vessel wall 850 so that a needle tip 832contacts the vessel wall 850. The needle 830 continues to move into thevessel wall 850 until a predetermined depth is reached. Here, thepredetermined depth is reached when the distal portion of the straingauge 840 contacts the vessel wall 850. As shown in FIG. 7, the straingauge 840 includes leads 844 extending from the strain gauge 840 to theproximal end of the needle.

An example of a strain gauge 840 that may be utilized with the presentinvention is a miniature semiconductor strain gauge manufactured byEntran. These strain gauges may be processed from P-type silicon inorientation, which provide maximum sensitivity to applied strain.Different strain gauges may also be available in other configurations.Different manufacturers may also produce similar strain gauges that arecapable of being utilized in the present invention. In order to preventfalse signals, the signal from the strain gauge should be offset orcalibrated to the appropriate level of force that the tissue is expectedto exert during successful tissue penetration. The force exerted by thetissue after successful needle penetration is much greater and longer induration than accidental contact with the needle sheath, catheterassembly or vessel wall. To minimize false signals further, the forcemeasurements should be taken only after the fluid delivery catheter 700has reached its intended destination.

FIGS. 7 a and 7 b illustrate the embodiment of the fluid deliverycatheter 800 of FIG. 7 in different positions with respect to the vesselwall 850. FIG. 7 a illustrates the fluid delivery catheter 800 where theneedle 830 has not yet contacted the vessel wall 850. The needle tip 832is close to and proximate to but not contacting the vessel wall 850.

FIG. 7 b illustrates the fluid delivery catheter 800 where a portion ofthe needle tip 832 is contacting and has become embedded in the vesselwall 850. The needle 830 is inserted a predetermined depth into thevessel wall 850. As seen in FIG. 7, the strain gauge 840 is attached tothe needle 830 at a predetermined distance from the needle tip 832. Whenthe needle 830 penetrates the vessel wall 850 a predetermined depth, thestrain gauge contacts the vessel wall 850 and senses contact pressurefrom the tissue. The contact pressure of the tissue thus signals to theoperator that a certain penetration depth of the needle 830 has beenachieved.

FIG. 8 illustrates an enlarged view of the embodiment of the needle 830and strain gauge 840 shown in FIG. 7. The strain gauge 840 is shownattached to the needle 830 a predetermined distance from the needle tip832. This allows the needle 830 to be inserted into the vessel wall ortissue to a predetermined penetration depth. In one embodiment, thepredetermined depth is 0.5 to 3 millimeters. In one embodiment, as shownin FIG. 8, the strain gauge 840 is covered by an encapsulant 842 toprotect the strain gauge 840.

Strain gauges are typically mounted very securely to the item that isexpected to deform or experience strain. Since the needle 830 isrelatively strong, it will not deform during tissue penetration and thesecurely mounted strain gauge 840 will not produce a signal. In oneembodiment, the strain gauge is embedded in a soft polymeric encapsulant842 before it is mounted on the needle 830. When the soft encapsulant842 makes contact with tissue during penetration, it deforms andtransfers this energy to the strain gauge 840. In one embodiment, thesoft polymeric material encapsulant 842 may be made of silicone. Inalternative embodiments, the encapsulant 842 may be made of otherbiocompatible materials.

FIG. 9 a illustrates an enlarged view of an alternative embodiment of aneedle 830 used in the fluid delivery catheter shown in FIG. 7. Here,the needle 830 has a stepped design with a distal (first) portion 834and a proximal (second) portion 836. The needle tip is 832 is located onthe distal portion 834. The distal portion 834 has a smaller diameterthan the proximal portion 836. In one embodiment, the distal portion 832has an outer diameter of 0.008 to 0.26 inches.

FIG. 9 b illustrates an enlarged view of an alternative embodiment of apiezoelectric transducer 840 for use in the fluid delivery catheter asshown in FIG. 7. The piezoelectric transducer 840 is shown with leads844. This piezoelectric transducer 840 is also seen in conjunction withthe needle 830 in FIG. 9 c. As seen in FIG. 9 c, the piezoelectrictransducer 840 is located on the stepped portion of the needle betweendistal portion 834 and the proximal portion 836 of the needle 830. Theencapsulant 842 is located around the piezoelectric transducer 840. Thestepped needle design is not necessary but may help to support thepiezoelectric transducer 840 and improve manufacturability.

In one embodiment, the distal portion 834 of the needle 830 may have anouter diameter of 0.008 to 0.26 inches and a proximal portion diameterof 0.012 to 0.3 inches. In alternative embodiments, these dimensions maychange according to application.

FIG. 10 illustrates a side view of one embodiment of a piezoelectrictransducer with a tubular shape 1040 connected to the needle 1030. Thepiezoelectric transducer 1040 is located a predetermined distance fromthe needle tip 1032 so that an operator may detect when the needle 1030has reached the desired penetration depth in the tissue.

In one embodiment the piezoelectric transducer 1040 may also be coveredby a soft encapsulant material as was shown for the strain gaugediscussed above in reference to FIGS. 7-9. In an alternative embodiment,the piezoelectric transducer may not be covered by the encapsulantmaterial.

FIG. 11 illustrates the flow chart of one embodiment of a process 1100of detecting tissue contact and needle penetration depth. At processingblock 1110 the syringe dispenses a therapeutic agent through the needle.

At processing block 1120, the needle dispenses a measured amount oftherapeutic agent from a second end of a needle to a first end of theneedle. At processing block 1130, the pressure of the therapeutic agentin the needle is measured. At processing block 1140, a first increase inpressure is measured when the first end of the needle contacts tissue.At processing block 1150, a second increase in pressure is measured asthe needle penetrates into the tissue to a predetermined depth.

Systems and methods for detecting tissue contact and needle penetrationdepth have been described. Although the present invention has beendescribed with reference to specific exemplary embodiments, it will beevident that various modifications and changes may be made to theseembodiments without departing from the broader spirit and scope of theinvention. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

1. A method of detecting tissue contact and a needle penetration depthof a needle used internally to deliver a therapeutic agent to a patientcomprising: dispensing a measured amount of therapeutic agent through alumen of a needle and from a second end of the needle to a first end ofthe needle at a predetermined flow rate, wherein the second end of theneedle is connected to a pressure measurement assembly; measuring apressure of the therapeutic agent in the needle wherein measuring thepressure includes; measuring a first change in pressure by measuring achange in the flow rate of the therapeutic agent dispensed through thelumen of the needle when the first end of the needle contacts a tissueand the first end of the needle becomes occluded; and measuring a secondchange in pressure when the needle penetrates the tissue further andwhen a first aperture located a predetermined distance from the firstend of the needle becomes occluded by measuring another change in theflow rate of the therapeutic agent dispensed through the lumen of theneedle, wherein said predetermined distance is used to specify a depthof the needle.
 2. The method of claim 1 wherein measuring pressure ofthe therapeutic agent in the needle includes measuring pressure of thetherapeutic agent using a pressure measurement assembly.
 3. The methodof claim 1 wherein the therapeutic agent is one of a drug, growthfactor, and gene therapy.
 4. The method of claim 1 wherein thepredetermined depth ranges between 0.5 and 10 millimeters.